The purpose of a gate valve is to control the flow of production fluids into or out of a well. Gate valves can be operated in various ways such as manually, hydraulically, pneumatically, and electrically. All operational models provide on-off flow control by aligning the gate, seat, and body flow bores (open) or aligning the solid part of the gate with the seat and body flow bores (closed). The gate makes a metal-to-metal seal with the seat and the seat makes a metal-to-metal and/or elastomeric seal with the valve body. Gate valves typically have a floating seat that is not rigidly held in place and the seat is captured within the seat pocket that has traditionally been a feature machined into the valve body. To operate the valve, the gate is moved up or down to either open or close the flow path.
Due to flow through the gate bore, movable parts, and operation of the valve there will be wear around the valve seat and even break downs and thus need for expensive maintenance and repair of the valve.
The patent application US2003015681 describes a valve sealing assembly comprising a first seat member (a pocket insert) and a second seat member (seat), with rear sealing rings and exterior annular retainer rings. The retainer ring on the pocket insert retains the pocket insert in the valve body and the retainer ring on the seat retains the seat in the pocket insert. The pocket insert comprises an exterior annular groove arranged to accommodate the retainer ring. The retainer ring is made of a flexible material, slightly oversized, to exert a force to the valve body and retain the pocket insert in the valve body. The retainer ring does not provide a seal but is preferably split to allow fluid flow around the ring. The pocket insert has an L-shaped cross section and accommodate the seat and make the interface between the seat and the valve body. The use of elastomeric seals requires low energization and seat may be press fitted as is or press fit using a retaining collar. This is a disadvantage due to the risk that it may loosen unexpectedly causing the system to be a seat, floating in a seat, floating in a seat pocket. Where “floating” is contained or captured but not rigidly restrained.